Apparatus for cutting bone

ABSTRACT

An apparatus ( 10 ) for cutting bone includes a shaft member ( 12 ) having a central axis ( 14 ) and extending between a proximal end portion ( 16 ) and a distal end portion ( 18 ). The proximal end portion ( 16 ) has a first surface ( 32 ) adapted to receive repetitive impacts. The distal end portion ( 18 ) includes a cutting blade ( 40 ) extending in a first plane between a shield section ( 46 ) and a guide portion ( 60 ). The shield section ( 46 ) and the guide section ( 60 ) project axially beyond the cutting blade ( 40 ) to recess the cutting blade ( 40 ) in the distal end portion ( 18 ). The shield section ( 46 ) includes an inwardly facing shield surface ( 48 ) which extends in a second plane that is transverse to the first plane of the cutting blade ( 40 ). The apparatus ( 10 ) is a form of an osteotome that is particularly useful for certain spine-related surgical procedures.

RELATED APPLICATION

The present application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/436,867, entitled PERCUTANEOUS CONTROLLEDVERTEBRAL OSTEOTOMY TOOL SET, filed Dec. 27, 2002.

TECHNICAL FIELD

The present invention relates to an apparatus for cutting bone and, inparticular, is directed to a uniquely designed osteotome that is usefulin cutting vertebrae.

BACKGROUND OF THE INVENTION

A known procedure for treating vertebral compression fractures and otherbone-related disorders is vertebral augmentation with bone cement.Vertebral augmentation can be performed by the direct-injection ofliquid cement into the collapsed vertebral body (commonly known as“vertebroplasty”). Vertebral augmentation can also be performed afterthe restoration of the vertebrae to near normal vertebral body anatomyand creation of an internal cavity with the use of an inflatable bonetamp. This minimally invasive procedure is commonly known as“kyphoplasty” (see, for example, U.S. Pat. Nos. 4,969,888 and5,108,404). During the kyphoplasty procedure, the inflatable bone tampis inserted through a small skin incision which accommodates a workingtube passed into the vertebral body. Inflation of the bone tampcompresses the cancellous bone and desirably moves the fracturedcortical bone to its pre-fractured orientation, creating a cavity withinthe vertebral body that can then be filled with a settable material suchas a cement or any number of synthetic bone substitutes. In effect, theprocedure sets the vertebral body at or near its pre-fracture positionand creates an internal cast, protecting the vertebral body from furtherfracture and/or collapse.

As compared to a traditional vertebroplasty procedure, kyphoplastyrestores the vertebrae to a pre-fractured condition and the injectedbone filler is less likely to leak out of the vertebral body during akyphoplasty procedure. However, under some circumstances, it has beenobserved that unpredictable reductions can occur with the kyphoplastytechnique in chronic or partially healed collapsed vertebral bodies.Under those circumstances, the surgeon would typically resort to alarge, open operation to re-align any post-traumatic kyphosis. Further,inadequate reductions can occur with certain other spinal deformitiessuch as scoliosis and kyphosis using the known techniques and surgicaltools. The large, open operations can carry with them significantmorbidity in an already physiologically compromised elderly population.The principle benefit of a percutaneous minimally invasive approach,which is the hallmark of the kyphoplasty procedure, is the minimalmorbidity associated with the procedure. In this light, additional toolsare required to further the kyphoplasty technique, achieve betteranatomic re-alignment of the spine, and maintain the minimally invasivenature of the surgery. The additional tools will be deployed throughsmall working portals and be able to achieve the desired strategicvertebral osteotomies to move bone in three dimensional space. One suchdesirable tool would provide a minimally invasive means to safely cutthe lateral (or side) wall of a vertebral body, such as a lateral wallwith a prior, and at least partially healed, compression fracture.

SUMMARY OF THE INVENTION

The present invention is an apparatus for cutting bone. The apparatuscomprises a shaft member having a central axis and extending between aproximal end portion and a distal end portion. The proximal end portionhas a first surface adapted to receive repetitive impacts. The distalend portion includes a cutting blade extending in a first plane betweena shield section and a guide section. The shield section and the guidesection project axially beyond the cutting blade to recess the cuttingblade in the distal end portion. The shield section includes an inwardlyfacing shield surface which extends in a second plane that is transverseto the first plane of the cutting blade.

The present invention further provides an apparatus for cutting throughthe cortical bone of a vertebral body, the cortical bone having an outerperipheral surface and an inner surface surrounding cancellous bone. Theapparatus comprises an elongate member having a shaft portion extendingalong a central axis between a proximal end portion and a distal endportion. The proximal end portion has a platform adapted to receiverepetitive impacts to advance the elongate member along the vertebralbody. The distal end portion of the elongate member includes an arcuatecutting blade extending in a first plane between first and second tipportions. The cutting blade is adapted to cut through the cortical boneof the vertebral body as the elongate member is advanced. The first tipportion has a shield surface which extends in a second plane that istransverse to the first plane of the cutting blade. The shield surfaceshields the cutting blade to prevent undesired cutting of soft tissuespresent on the outer peripheral surface of the vertebral body. Thesecond tip portion comprises a blunt tooth extending generally parallelto the central axis and acting as a guide to ensure that the distal endportion of the elongate member follows the contours of the inner surfaceof the vertebral body as the elongate member is advanced.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will becomeapparent to those skilled in the art to which the present inventionrelates upon reading the following description with reference to theaccompanying drawings, in which:

FIG. 1 is a side view of an apparatus for cutting bone constructed inaccordance with the present invention; FIG. 2 is a plan view taken alongline 2-2 in FIG. 1;

FIG. 3 is a plan view illustrating the apparatus of FIG. 1 being used tocut a lateral wall of a vertebral body; and

FIG. 3 is a side view taken along line 4-4 in FIG. 3, with soft tissueson the outside of the vertebral body omitted for clarity.

DESCRIPTION OF EMBODIMENTS

The present invention relates to an apparatus for cutting bone and, inparticular, is directed to a uniquely designed osteotome that is usefulin cutting vertebrae. As representative of the present invention, FIGS.1 and 2 illustrate an apparatus 10 comprising an elongate member 11 madeof a medical grade metal such as stainless steel. The elongate member 11includes a shaft portion 12 extending along a central axis 14 between aproximal end portion 16 and a distal end portion 18 of the apparatus 10.In accordance with one embodiment of the invention, the shaft portion 12and the distal end portion 18 are designed to fit through a 5 mm (innerdiameter) cannula 20 (FIG. 3) and thus have a maximum outer diameter of4.8 mm. It should, however, be understood that the apparatus 10 and thecannula 20 could have correspondingly larger or smaller diameters.

The proximal end portion 16 of the apparatus 10 has a platform 30 with aplanar surface 32 adapted to receive repetitive impacts from anothertool, such as a hammer (not shown), to advance the elongate member 11.The platform 30 has a larger outer diameter than the shaft and distalend portions 12 and 18 of the apparatus 10 to facilitate receivingimpacts with a hammer.

The distal end portion 18 of the apparatus 10 includes an arcuatecutting blade 40 (FIG. 2) extending in a first plane between first andsecond tip portions 42 and 44. The cutting blade 40 is recessed axiallyfrom the terminal ends of the tip portions 42 and 44 and is adapted tocut through cortical bone as the elongate member 11 is advanced. Thefirst tip portion 42 comprises a shield section 46 having a shieldsurface 48 (FIG. 1). The shield surface 48 extends in a second planethat is transverse to the first plane of the cutting blade 40. In theembodiment of FIGS. 1 and 2, the shield surface 48 is perpendicular tothe cutting blade 40. As may be seen in FIG. 1, the shield section 46 atthe distal end portion 18 is approximately the same width (or diameter)as the shaft portion 12 of the apparatus 10. The shield section 46further includes an arcuate end surface 50 and an outwardly facing rampsurface 52 (FIG. 2). It is contemplated that the end surface 50 couldalso be sharp similar to a periosteal elevator.

The second tip portion 44 comprises a guide section 60 that extendsgenerally parallel to the central axis 14. The guide section 60 includesa blunt tooth 62 with a bulbous terminal end 64. As may be seen in FIG.1, the guide section 60 is substantially narrower in width (or diameter)than the shield section 46 and projects axially beyond the end surface50 of the shield section.

FIGS. 3 and 4 illustrate use of the apparatus 10 to cut bone.Specifically, FIGS. 3 and 4 illustrate the apparatus 10 cutting throughcortical bone 70 of a vertebral body 72. The cortical bone 70 of thevertebral body 72 has an outer peripheral surface 74 and an innersurface 76 that surrounds cancellous bone 78. As best seen in FIG. 4,the vertebral body 72 has a partially healed compression fracture to betreated via a kyphoplasty procedure. In order to perform the kyphoplastyprocedure, the partially healed cortical bone 70 in the lateral wall 80of the vertebral body 72 must be cut to release the upper and lower endplates 82 and 84 of the vertebral body so that an inflatable bone tamp(not shown) inserted inside the vertebral body can, when inflated, movethe upper and lower end plates back to their pre-fractured positions(illustrated in dashed lines in FIG. 4).

Access to the lateral wall 80 of the vertebral body 72 occurs in aminimally invasive manner via the cannula 20. After drilling a passagethrough a transverse process 86 of the vertebral body 72, the cannula 20is placed through the transverse process. The distal end portion 18 ofthe apparatus 10 is then inserted through the cannula 20 and intoengagement with the lateral wall 80 of the vertebral body. Next, theblunt tooth 64 of the guide section 60 is tapped through the corticalbone 70 of the vertebral body 72 so that the cutting blade 40 ispositioned to cut the cortical bone as shown in FIG. 3.

From the position of FIG. 3, the distal end portion 18 of the apparatus10 is advanced along the lateral wall 80 of the vertebral body 72through impact blows, either by hand, hammer, or other suitable means tothe platform 30 at the proximal end portion 16. As the distal endportion 18 advanced, the cutting blade cuts the lateral wall 80 in orderto release the end plates 82 and 84 of the vertebral body 72.Significantly, the bulbous terminal end 64 of the guide section 60follows the contours of the inner surface 76 of the cortical bone 70 andprevents the distal end portion 18 from straying out of engagement withthe vertebral body 72 as the distal end portion is advanced.

Furthermore, as the distal end portion 18 of the apparatus 10 isadvanced, the shield surface 48 acts as a shield for the cutting blade40 to prevent undesired cutting of soft tissues 90, such as bloodvessels, nerves, and muscles, present on the outer peripheral surface 74of the vertebral body 72. In addition, as the distal end portion 18 isadvanced, the arcuate end surface 50 of the shield section 46 slidesunderneath the soft tissues 90 on the outer peripheral surface 74 of thevertebral body 72 and cooperates with the ramp surface 52 to lift thesoft tissues off of the outer peripheral surface. This geometry at thedistal end portion 18 allows the apparatus 10 to safely cut the lateralwall 80 so that a kyphoplasty procedure can be used to treat thecompression fracture of the vertebral body 72 in a minimally invasivefashion.

From the above description of the invention, those skilled in the artwill perceive improvements, changes and modifications. For example, itshould be understood that, depending on the nature of the condition of agiven vertebral body, the lateral wall on the opposite side of thevertebral body 72 shown in FIG. 3, or on both sides of the vertebralbody, may need to be cut in order to release the end plates of thevertebrae. In such situations, the apparatus 10 would be used in anidentical fashion with access through a cannula placed through the othertransverse process. Further, it should be understood that the apparatus10 disclosed herein could be used to cut through other areas of corticalbone in vertebrae, as well as cortical bone in other bones in amammalian body. Such improvements, changes and modifications within theskill of the art are intended to be covered by the appended claims.

1-12. (canceled)
 13. A method for cutting bone, the bone having an outerperipheral surface and an inner cortical surface, said method comprisingthe steps of: providing an apparatus comprising a shaft member having acentral axis and extending between a proximal end portion and a distalend portion, the distal end portion including a cutting blade extendingin a first plane between a shield section and a guide section, the guidesection including a bulbous terminal end, the shield section and theguide section projecting axially beyond the cutting blade to recess thecutting blade in the distal end portion, the shield section including aninwardly facing shield surface which extends in a second plane that istransverse to the first plane of the cutting blade; positioning theapparatus so that the distal end portion of the engages the outerperipheral surface of the bone; and repetitively impacting the proximalend portion of the apparatus so that the cutting blade cuts the bone.14. The method of claim 13 wherein said step of repetitively impactingthe proximal end portion of the apparatus further comprises the step ofsliding an arcuate end surface of the shield section underneath softtissues present on the outer peripheral surface of the bone as the shaftmember is advanced, the shield surface functioning as a shield for thecutting blade to prevent undesired cutting of the soft tissues.
 15. Themethod of claim 14 wherein said step of repetitively impacting theproximal end portion of the apparatus further comprises the step ofusing the shield section, which includes an outwardly facing rampsurface for cooperating with the arcuate end surface, to lift the softtissues off of the outer peripheral surface of the bone as the shaftmember is advanced.
 16. The method of claim 13 wherein said step ofpositioning the apparatus so that the distal end portion of theapparatus engages the outer peripheral surface of the bone furthercomprises the steps of: providing a cannula to facilitate delivery ofthe apparatus; inserting the apparatus into the cannula; and tapping theproximal end portion of the apparatus so that the blunt tooth of theguide section penetrates the outer peripheral surface of the bone, theguide section comprising a blunt tooth extending generally parallel tothe central axis and acting as a guide to ensure that the distal endportion of the shaft member follows the contours of the inner corticalsurface of the bone as the shaft member is advanced.
 17. A method forcutting through the cortical bone of a vertebral body having upper andlower end plates, the cortical bone having an outer peripheral surfaceand an inner surface surrounding cancellous bone, said method comprisingthe steps of: providing an apparatus comprising an elongate memberhaving a shaft portion extending along a central axis between a proximalend portion and a distal end portion, the distal end portion of theelongate member including an arcuate cutting blade extending in a firstplane between first and second tip portions, the first tip portionhaving a shield surface which extends in a second plane that istransverse to the first plane of the cutting blade, the second tipportion comprising a blunt tooth extending generally parallel to thecentral axis and a bulbous terminal end; forming a passage through atransverse process of the vertebral body to access a lateral wall of thevertebral body; inserting the apparatus into the passage so that thedistal end portion engages the lateral wall of the vertebral body; andimpacting the proximal end portion of the apparatus so that the distalend portion is advanced along the lateral wall of the vertebral body andthe cutting blade cuts the lateral wall to release the end plates of thevertebral body.
 18. The method of claim 17 wherein said step ofrepetitively impacting the proximal end portion of the apparatus furthercomprises the step of sliding an arcuate end surface of the shieldsection underneath soft tissues present on the outer peripheral surfaceof the bone as the shaft member is advanced, the shield surfacefunctioning as a shield for the cutting blade to prevent undesiredcutting of the soft tissues.
 19. The method of claim 18 wherein saidstep of repetitively impacting the proximal end portion of the apparatusfurther comprises the step of using the shield section, which includesan outwardly facing ramp surface for cooperating with the arcuate endsurface, to lift the soft tissues off of the outer peripheral surface ofthe bone as the shaft member is advanced.
 20. The method of claim 17wherein said step of inserting the apparatus into the passage furthercomprises the steps of: inserting a cannula into the passage; andtapping the proximal end portion of the apparatus so that the blunttooth of the guide section penetrates the outer peripheral surface ofthe cortical bone, the second tip portion including a bulbous terminalend that helps the second tip portion follow the contours of the innersurface of the vertebral body as the elongate member is advanced. 21.The method of claim 17 further comprising the step of cutting thecortical bone to release the upper and lower plates of the vertebralbody and inserting an inflatable bone tamp inside the vertebral body sothat the upper and lower end plates back to their pre-fracturedpositions when the inflatable bone tamp is inflated.